Transmitting system



May 2, 1933. c. w. HOQGH 1,906,269

TRANSMITTING SYSTEM Filed Feb; 7, 1929 5 Sheets-Sheet 1 May 2, 1933. c w HOUGH 1,906,269

TRANSMITTING SYSTEM Filed Feb '7, 1929 5 Sheets-Sheet. 2

M y 2, 1933- c. W. HOKYJGH 1,906,269

TRANSMITTING SYSTEM Filed Feb; 7, 1929' 3 Sheets-Sheet 3 g u m \57 all) Patented May 2, 1933 naive stares afar FFEE CLINTON XV. ROUGH, F BOONVILLE, NEW YORK, ASSIGNOR, BY lvfESNE ASSIGNMENTS, TO WIRED BABE-5, INCL, GE" N i N YORK, N. Y., A COBPGRATION OF DELAWARE TRANSMITTING SYSTEM;

pplicatic-u filed February 7, 1929.

My invention relates to transmitting and receiving systems in general and more specifically to systems employing continuous wave high frequency electrical energy.

An object of my invention is to provide an improved transmitting and receiving system employing thermionic tubes whereby a plurality of messages or programs may be transmitted and received by employing a single carrier frequency.

Another object of my invention is to provide a transmitting system whereby each side band is modulated at a different audio frequency.

Still another object of my invention is to provide a receiving system whereby either side band modulation may be received without interference from the other side bands.

ther and further objects of my invention reside in the circuit arrangements to produce the desired operation. A better understanding of the transmitting and receiving system of my invent-ion can be had by referring to the specification following and to the accompanying drawings wherein: Figures 1 and 2 are schematic circuit diagrams showing the transmitting system of my invention; Fig. 3 is a schematic circuit diagram showing the receiving system of my invention and Figs. 4 and 5 are graphical representations showing the operation of the transmitting and receiving system of my invention.

The objects of this invention are somewhat similar to those of my application, Serial No. 328,009, which on June 14:, 1932 issued into Patent No. 1,863,374. That patent discloses means for transmitting two distinct signals on one carrier wave; Such means, however, include a frequency multiplier to produce a carrier wave upon which alternate and separately modulated half cycles of a fundamental frequency may be superposed. From the description to follow, the manner of carrying out the instant invention will, therefore, be readily distinguished from the disclosure of the said patent.

In continuous wave transmitting systems for the transmission of audio frequencies Serial No. 338,146.

such as voice or music, he high frequency carrier wave produced by thermionic tubes and their associated circuits is varied in arm plitude'corresponding to variations of the audio frequencies. A carrier wave of 100 kilocycles may be said to be modulated at 100 plus kilocycles and 100 minus 10 kilocycles. Such an illustration is exaggerated as compared to the narrower modulation which is usually the case. The above values, plus 10 kilocycles and minus 10 kilocycles will serve however for the purpose of ex planation. Many complete cycles of the transmitted carrier have nearly the same amplitude due to the. higher frequency modulated by a frequency of lower order. lhermionic tubes are usually employed in the receiving system which serve to amplify and rectify the incoming signaling energy. In most transmitters of the above mentioned type, both side bands have corresponding modulations. In the transmitting and receiving system of my invention each side band is modulated by an individual group of audio frequencies and is selectively received at the receiving station. A better understanding can be had of the system of my invention by referring to the specification following and to the accompanying drawings.

Figure 1 is a schematic circuit diagram showing one form of the transmitting system of my invention. Thermionic tubes 1 and 2 are employed as modulators and may be of the type employing cathodes, anodes and control electrodes. Any suitable thermionic tubes may be employed including tubes having four or more electrodes. Thermionic tube 16 is employed in an oscillatory circuit arrangement including inductance a in the input circuit and'inductances 13, 11, 12, 15 and 14 in the output circuit. Inductances 15 and 15a may be placed in inductive relation or may be in a non-inductive relation and each individually adjusted to the proper frequency value. Capacity 13a may be employed to control the frequency. characteristics'of the circuit 11, 12, 13', 14 and 15 and also control the value of energy in this circuit.

Thermionic tubes 1 and 2 are modula- .100

tors and are associated with sources of audio frequency 9 and 10 respectively. The output circuit of modulator 1 includes inductance 6 and source of anode supply potential 38. The output circuit of modulator 2 includes inductance 7 and source of anode potential 8. The input circuits of modulators 1 and 2include inductances 3 and 1 respectively and common source of control electrode potential 5. The cathodes of thermionic tubes 1 and 2 may be connected to ground if necessary to produce the desired energy node. In this manner alternating potential would be supplied to the control electrodes of thermionic tubes 1 and 2. During one complete cycle, the control electrode of thermionic tube 1 would be impressed with a positive potential followed by negative potential in respect to the cathode circuit. Likewise thermionic tube 2 would have a negative potential impressed upon the control electrode followed by a positive potential in respect to the cathode circuit. Source of control electrode biasing potential 5 may be adjusted to cause thermionic tubes 1 and 2 to operate on the proper portion of their characteristic curves. In this manner the energy of alternating polarity from inductance 11 would cause the resistance of thermionic tubes 1 and 2 to alternately increase and decrease in value. Any suitable method may be employed whereby the blocking and unblocking of thermionic tubes 1 and 2 causes the modulation of the upper and lower side bands respectively. The method shown in Fig. 1 is essentially that of absorption. Inductances 6 and 7 are related to the output energy from oscillator 16 in such a manner that the output circuits of thermionic tubes 1 and 2 absorb energy from inductances 12 and 13 respectively. The amount of energy absorbed by the output circuits of thermionic tubes 1 and is a function of the an ode-cathode resistance. The anodecathoc.e resistance depends upon the impressed control electrode potential from inductance 11. Source of biasing potential 5 is adjusted to cause the resistance of thermionic tubes 1 and 2 to alternate in value. Thus the resist ance between the cathode and anode of thermionic tube 1 will be of a high order and which when excited by potential of opposite polarity will be of a low order. Similarly the anode-cathode resistance of thermionic tube 2 will be of a low order which when eX- cited by potential of opposite polarity will be of a high order. The resistance of thermionic tubes 1 and 2 alternating through this cycle of values whereby the resistance of the one is high when the resistance of the other is relatively low, the absorption by circuits 6 and 7 from 12 and 13 will alternate. This absorption is alternated between tubes 1 and 2 depending upon their respective internal resistances. As an example, assume that the characteristics of thermionic tubes 1 and 2 are such that when the respective control electrodes are supplied with a negative potential of the order of five the anode-cathode resistance is comparatively high. Assuming further that the dynamic portion of the characteristic curve of such a tube is employed, when the negative potential of the control electrode is changed to the order of four, there results a corresponding decrease in the anode-cathode resistance. The absorption of energy by the circuit comprising these electrodes would be correspondingly increased. This decrease in the value of negative potential in the control electrode circuit would result were the polarity impressed on this circuit from the oscillator of a positive value. The following half cycle would be of a negative polarity which when impressed on this circuit would cause no appreciable change in the anode-cathode resistance of the tube and would effect no increased absorption from the oscillator circuit. The potential of positive and negative polarity is simultaneously impressed upon thermionic tubes 1 and 2. Immediately following the opposite polarity is impressed upon each respective tube. Thus tube 1 is operative causing an absorption in its associated output circuit when tube 2 is inoperative or non-absorptive. The next instant the converse is true. The change in re sistance of the output circuit of each thermionic tube during alternate half cycles is further augmented by sources of low frequency energy 9 and 10 thereby causing one side band of modulation by source 9 and the remaining side band of modulation by source 10. Any suitable load circuit 18, comprising suitable amplifiers, space radio radiating systems or wired radio systems may be associated with inductance 14. In this manner each individual side band of modulation is by an individual audio frequency and the resultant may be amplified in common by the usual amplifier circuit arrangement.

Fig. 2 shows a schematic circuit arrangement of the transmitting system of my invention embodying certain modification of the circuit arrangement shown in Fi 1. In this circuit arrangement thermionic tube modulators 1 and 2, similar to modulators 1 and 2 of Fig. 1, serve to produce the respective side bands of modulated energy. Thermionic tube 16 is employed in an oscillatory circuit comprising inductances 15, 15a, 8 and 14. Inductances 6 and 7 associated with inductance 8 comprise the anode circuits of thermionic tubes 1 and 2 respectively. Source 21 supplies the necessary anode potential for thermionic tubes 1, 2, 16 and 16a. The input circuits of thermionic tubes 1 and 2 comprise inductances 3 and 4 respectively which are inductively coupled in opposite sense to inductance-11. Inductances 3 and 4 are associated with sources oflow frequency energy?) and 10 respectively. The input circuit of thermionic tube 16a fincludes inductance '13 l and source of control electrode energy 20. inductance 13 is associated with the output of thermionic tube 16. "High frequency electrical energy is amplified by thermionic tube 16a and is transferred to the inputcircuits of thermionic tubes l andQ by means of inductance 11. lnductance 11 is herein shown as two individual inductances for the purpose of showing the relative distribution of energy transferred to inductances 4t and 3. The-rmionic tube 16a operates as a modulation control whereby-acoutrol is had of'the energy transferred to :the input circuits of modulators 1 and 2. The operational characteristics of thermionic tubes 1 and 2 may be varied by means of sources of control electrode biasing potential 5 and'5a respectively; Load circuit 18 is associated with inductance 14.- Load circuit 18 may comprise suitable amplifier circuits, a wired radio circuit or a space radio radiating circuit. The operation of lthe transmitting circuit is fundamentally similar to the operation of the circuit arrangement shown in Fig. 1 with the modificationfin that the circuit arrangement shownin the latter illustration employs a' means for controlling the energy-normally transferred to the modulator tubes irrespective ofthe energy generated in-the oscillatory circuit- 1 Fig. 3 of theaccompanying': drawings shows a scheniatic, circuit-diagram of the receiving part-of the transmitting and re ceiving system of my invention. v Th-ermionic tube 22 may be of any suitable designincluding the three electrode type illustrated. Thermionic tube 22' has a cathode23, control electrode 25and anode'24; Thermionic tubes having four or more electrodesmay be employed. The output circuitof thermionic tube 22 includes reproducer 30 and source of anode supply potential 29. .The input circuit of thermionic tube 22 includes inductance 26,-polarity reversing switch'2'7 and sourceof potential 28. ,An energy collecting circuit 31 is associated withthe inputcircuit of thermionic tube22. This circuit 31-may also include suitable amplifier circuits. The operation of the receivingcircuit can best be understood by referring to Figsd and 5. l l

Fig. 4 of the accompanying drawings is a graphical illustration showing the carrier wave and side bands ofmodulation produced by the transmitting system of my invention. Thehigh frequency energy is known as the carrier frequency 35, the amplitude ofwhich is modulated by frequencies of the lower order 36 and 37 which latter are known as modulating frequencies. From observation the wave form is seen to be unsymmetrical; This is because of the different and individual modulating frequencies producing thev upper thought of as; the modulation of amplitude o'fthe'positive :half of the cycles of high frequency energy and that of the lower side band '37 the modulations of amplitude of the negative half of the cycles of high frequency energy. Fig. 5 ofthe accompanying drawings shows a" graphical representation of the operation of the receiver .for receiving the signaling energy graphically represented in Fig. 4.

The illustration shows a.characteristic curve of the thermionic tube operationalxcharacteristics ofthe type employed in 'the receiving system. Here the anode current 110' is plotted against the control electrode potential Eg. The control electrode potential egis common with the axis Eg which represents theioperation of the thermionic tube when the switch 27 shown in Fig. 3 is in one position. The controlel-ectrode potential eg is common with the axis Eg which represents the operationof the thermionic tube .when the "switch member 27, is in. the other position. The two positions of'switch'member 27 profvide means for reversing theimpressed conitrol electrode biasing potential. With a thermionic tube having a characteristlc curve as shown in Fig. 5, eli'icient rectification of the .signalingenergycanbe had. In order that efiicient rectification is accomplished it :is

necessary'that the control electrode of the thermionic tube operate at the normal potentialEg orEgQ Either of these positions would result inrectification of the signaling energy. The control-"electrode potential might be reduced to O in which case no rectification of appreciable amount would result.

The latter adjustment is represented bythe anode current shown indottedl'ines. The anode current when. the normal control electrode potential is E9 is shown by the line I T The anode current when the normal control electrode potential-is Eg" is shown by theline Tp.- The resultant. anode current is shown by the signs 11pand 10 for the 'two adjustments respectively.

As an illustration assume that the normal controlelectrode potential is of the order of Eg. and-the'incoming signaling energy of the order of eg. The negative half of the cycle would cause a change in the anode cur- -,rent i from :the normal value 129 tothe amount 1. The-following positive half of -"the'cycle would subtract from the normal control electrode potential E9 causing a change of 4 in. the anode current z'p. By operating the control electrode at a normal 'potentialof the order of E9; the change 7179 inthenormal anode current 112 during the negative half of the cycle would be of the order of 7 while the positive half'of the cycle of theincomingsignal cg would cause a "In -pa employed'in suitable cascade arrangement whereby complete rectification is produced.

When theincoming signaling energy'is not modulated more than twenty percent the selective rectification may be efliciently and completely accomplished.

I realize that many modifications of the transmitting and receiving system of my invention .arepossible without departing from the spirit of my invention. For instance amplifiers may be .employed in the low frequency source of modulating frequencies at the transmitter. Four-electrode tubes or tubes having more than four electrodes may be employed. Batteries are shown in the accompanying drawings, however, it is obvious that any suitable supply of electrical energy maybe employed in their stead. The receiver may comprise high frequency ther-' mionic tube amplifier stages preceding the detector or rectifier, followed by selectively adjusted balanced audio frequency amplifier circuits. i j

his .to be understood that the numerical values chosen in the foregoing specification and shown in the accompanying drawings are arbitrary and it is to be further understood that my invention shall not be restricted to the foregoing specification or to the ac'-' companying drawings but only as defined in the appended claims. What I claim as new and desire to secure by Letters Patent of the United States is as follows: l

1. A transmitting system comprising a thermionic tube oscillatory circuit, means for establishing an energy node in said circuit, means for causing the energy on each side of said node to energize individualcontrol elec trodes of-other thermionic tubes, independent'ymodulated output circuits associated with said last mentioned tubes and coupled respectively with each side of said oscillatory circuit, said last mentioned tubes being alternately absorptive of'energy from said oscillatory circuit.

2. A transmitting system comprising in combination a thermionic tube oscillatory circuit for generating high frequency electrical oscillatory circuit, said last mentioned tubes being alternately absorptive of" energy from said oscillatory circuit.

3.,A transmitting system comprising in combination athermionic tube oscillatory cir cuit for generating oscillations of high frequency electrical energy, means for establishing a potential node of said energy and antinodes of energy on each side of said node in said oscillatory circuit, means for admitting energy from said individual antinode positions to the individual input circuits of indisaid oscillatory circuit, means for admitting energy from said individual. antinode positions to the individual input circuits of individual thermionic tubes, the internal resist 'a'ncel of said .last mentioned tubes being changed only by one half cycle of said high frequency energy, means for independently modulating the energy in the respective output circuits of said last mentioned tubes and coupling means for alternately transferring the modulated energy of said output circuits back to said oscillatory circuit.

5; A transmitting system comprising in combination a thermionic tube oscillatory circuit-for generating oscillations of high frequency electrical energy, means for establishing a potential node of said energy and antinodes ofenergy on each side of said node in said oscillatory circuit, means for admitting energy from said-individual antinode positions to the individual input circuits of individual thermionic tubes, the internal resist ance of said last mentioned tubes belng.

changed only by one half cycle of said high frequency energy, means for varying theresistance of said last mentioned tubes by individual sources of low frequency energy and means for associating the output circuits of said last mentioned tubes with said oscillatory circuit. 7

6. The method of transmitting'two distinct signals on one carrier wave which comprises generating high frequency energy, establishing a potential nodal point in the circuit thereof, independently impressing signal modulations upon said circuit at antinodal points on, either side of said nodal point, 10- callyv absorbing said high frequency energy from that portion of the circuit to one side of the nodal point which has negative potential and transmitting the modulated energy from that portion of the circuit to the other side.

of said nodal point which has positive potentia 7 A transmitting system comprising a thermionic tube oscillator having a high frequency oscillatory circuit, means for establishing a potential node of energy in said circuit, antinodes of energy on each side of said node, a pair of thermionic tubes having control electrodes in circuit with means coupled to opposite sides of said nodal point respectively, an anode circuit for each of said last mentioned tubes coupled to said oscillatory circuit at antinodal points on opposite sides of said node, means for independently modulating each of said anode circuits and means for increasing the internal resistance of said last mentioned tubes to inoperativeness alternately in synchronism with the half cycles of said high frequency energy.

In testimony whereof I affix my signature.

CLINTON W. HOUGH. 

